JPS6026527B2 - Biological electrode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a biological electrode for deriving biological electrical phenomena such as electrocardiograms and electroencephalograms.

Electrical phenomena occurring in living organisms are extremely weak, for example, several mV in an electrocardiogram and several tens of muV in an electroencephalogram.

These biological signals are generally extracted with electric potentials such as silver-plated electrodes attached to the epidermis of the living body, and amplified and recorded by an external device such as a shingume meter via lead wires. However, the contact resistance of the electrode with the skin (hereinafter referred to as "electrode impedance") includes the electrical resistance of the biological epidermis (hereinafter referred to as skin impedance Zd) and the electrode resistance (hereinafter referred to as electrode impedance).
The contact impedance (hereinafter referred to as contact impedance) is said to be from several MO to several MO, and in order to faithfully detect weak biological signals, an amplifier with an input impedance sufficiently larger than this contact impedance is required, and ideally it is infinite. Large is preferable.

However, in measuring instruments with high input impedance, the signal waveform is disturbed by the slightest shaking of the electrode lead wire or movement of the electrode due to body movement, and noise at the commercial frequency mixes into the signal waveform, which interferes with measurement.

Therefore, there is a limit to increasing the input impedance of the amplifier, and for electrocardiographs, it is set to about 8 MO. Therefore, it was necessary to make the contact impedance of the electrode as low as possible. For this reason, some conventional electrodes extract electric potential by interposing an electrode paste containing electrolyte between the biological epidermis, but even with this, there is a limit to reducing the impedance of the contact resistance, and the electrode paste can be used for long periods of time. When used, the base dried and conversely the contact impedance increased and the signal waveform became unstable.

Another drawback was that the electrode base caused skin irritation.
In addition, as another example of an electrode, an electrode in which the electrode lead wire is shielded is effective against shaking of the lead wire, but since stray capacitance Cs and leakage resistance Rs exist between the shield side of the shield wire and the core wire. Even if an amplifier with infinite input impedance is used, there is a drawback that the input impedance Zin decreases to Zin=Rs/(CsRs+1 of i) due to the shielded wire. In addition, there is a device with a double electrode structure, including a first electrode plate for detecting biological signals, and a second electrode plate surrounding the first electrode plate, which is provided on the same plane as the electrode plate and connected to the ground. be. However, this has the disadvantage that when worn on the skin, the first electrode plate at the center is connected to the second electrode plate due to skin resistance and grounded, making it impossible to maintain a high input impedance. Furthermore, when sweating, the input side may become short-circuited due to the sweat, making it impossible to derive a signal waveform. Another type of electrode is one in which a semiconductor active element circuit is directly incorporated into the electrode, the impedance of the biological signal is converted by the electrode itself, and the low-impedance signal is derived through a lead wire.

However, although this is superior in terms of high input impedance, it lacks the safety of the baseline of the guided waveform and has the disadvantage that even the slightest body movement causes the waveform to become distorted and is difficult to handle.

Furthermore, in order to reduce the effects of artifacts on this type of electrode, some types cover the back of the electrode with a shielding material, but this reduces the input impedance because the input leakage current flows through the shield to the ground. Its value as a seed electrode had been halved. The present invention was developed in view of the above drawbacks, and is capable of always extracting a stable waveform while maintaining an extremely high input impedance. The impedance of the detected biological signal is converted, and the output side is applied to the guard electrode that surrounds the sensitive electrode in a ring shape to make it have the same potential as the sensitive electrode. The object of the present invention is to obtain a biological electrode with extremely high input impedance.

Embodiments of the present invention will be described below with reference to the drawings.

Figure 1 is a cross-sectional view of the biological electrode of the present invention, and Figure 2 is a cross-sectional view of the biological electrode of the present invention.
FIG. 2 is an equivalent circuit diagram of FIG.

In the figure, the biological electrode 1 includes a sensitive electrode 2 with a rounded surface to be attached to the epidermis of the living body, a guard electrode 3 arranged in a ring shape around the sensitive electrode 2, and these sensitive electrodes 2 and the guard electrode integrated. an insulating electrode holder 4 held on the electrode holder 4; a high voltage protection circuit 5 mounted on the electrode holder 4 and housed in the guard electrode 3; It has at least an impedance conversion circuit 6 connected thereto.

The sensitive electrode 2 may be made of, for example, a metal such as silver, chloride wire, stainless steel, or gold, a semiconductor such as silicon, a conductor such as silicon oxide or barium titanate, a polymer material such as carbon resin,
Or a composite material made of a combination of these is used.

The guard electrode 3 may be made of the same material as the sensitive electrode, and in this embodiment, it is disposed in a cup shape on the opposite side of the electrode holder 4 from the sensitive electrode 2 so as to cover the sensitive electrode from the outside. The electrode holder 4 is made of epoxy resin or the like to maintain electrical insulation. The high voltage protection circuit 5 is designed to protect the high voltage from being introduced to the impedance converter 6 or the electrocardiograph (not shown) through the sensing electrode 2 by using a defibrator or the like. It is. In FIG. 2, the high voltage protection circuit 5 includes resistors 51 and 52, and Zener diodes 53 and 54 connected in reverse to each other between the connection point of these resistors and the ground terminal 7.

Resistors 51 and 52 are selected from 1pi○ to 1piQ, but the sensitive electrode 2
The resistor 51 can be omitted if a material with a relatively high resistivity of about 10-1 to 1 pcm is used.

Further, the sensor diodes 53 and 54 exhibit high resistance when a weak biological signal is introduced. However, the Jenner voltage (
Generally, when a voltage of several volts or more is introduced, the resistance drops rapidly, and the current at this time is led to the ground terminal 7 via the resistor 51 and the Jenner diodes 53 and 54. Therefore, the impedance conversion circuit 6 is prevented from being damaged.
The impedance conversion circuit 6 consists of an operational amplifier 61, one input side of which is connected to the resistor 52 of the high voltage protection circuit 5, and the output of the operational amplifier 61 is fed back to the other input side.

8 is a terminal of a power source that drives the operational amplifier 61.

The output side of the operational amplifier 61 is led to an external device (not shown) via a lead wire 9 and is also connected to the guard electrode 3. Note that the high voltage protection circuit 5 is not necessarily required, and if necessary, it may be manufactured as a single element by integrating it with the impedance conversion circuit 6 using IC technology or the like. Furthermore, the sensitive electrode 2 may be formed of a semiconductor such as silicon, and the impedance conversion circuit 6 and the high voltage protection circuit 5 may be integrally formed on one or both surfaces thereof. Next, the operation of the above embodiment of the present invention will be explained.

A biological electrode 1 attached to the epidermis of a living body extracts a weak biological signal via a crab-sensitive electrode 2.

This biosignal is guided to the high voltage protection circuit 5 which is directly connected to the sensitive electrode 2, but if the input voltage is below the Zener fin pressure of the Zener diodes 53, 54, the resistor 51,
Operational amplifier 61 of impedance converter 6 via 52
is used as one input.

Accordingly, this operational amplifier is driven by a power supply connected to the terminal 8, and the biopotential is impedance-converted and derived from the output side 62 thereof. At this time, since this output side 62 is connected to the guard electrode 3 at the same time, even if leakage impedance Zs due to stray capacitance Cs and leakage resistance Rs exists between the sensitive electrode 2 and the guard electrode 3, the guard electrode 3 is connected to the input It is kept at the same potential as the voltage. Therefore, no input leakage current occurs and an apparently extremely high input impedance is maintained. Next, when a high voltage is applied to the living body using a defibrillator, the impedance converter 6 is prevented from being damaged because the Zener diodes 53 and 54 operate as described above and are connected to the ground.

FIG. 3 shows another embodiment of the present invention, in which a guard electrode 3 is integrally bonded to cover the back surface of an electrode holder 4, and shields the sensitive electrode 2 from the outside in an annular shape. It is something.

FIG. 4 shows yet another embodiment in which a guard electrode 3 is fitted into an electrode holder 4 and arranged in a ring shape with the sensing electrode 2 at the center.

FIG. 5 is a bottom view at this time. FIG. 6 shows still another embodiment of the present invention, in which a hole 11 is provided at an arbitrary location in a groove 10 between a sensing electrode 2 and a guard electrode 3 of an electrode holder 4.

As a result, sweat adhering to the sensitive electrode 2 and the guard electrode 3 is released to the outside of the electrode through the hole 11, and electrical connection between the sensitive voltage 2 and the guard electrode 3 is avoided. This promotes the purpose of lowering the impedance of the output signal. In the present invention, even if the high voltage protection circuit 5 is not provided and the shielded side of the shielded wire is directly connected to the output of the impedance converter 6 without being grounded, various artifacts may occur due to the extremely low output impedance. Naturally, the same effect as when the shielded side of the shielded wire is connected to the ground can be obtained.

As described above, when the present invention is used, the output is made low impedance by impedance conversion, so there is no need to lower the contact impedance using electrode paste.

Moreover, since this guard electrode is driven by an impedance converter with an extremely low output impedance, it has a strong shielding effect against various artifacts, and no hum is mixed in. In addition, the biological electrode of the present invention can be expected to have the same effect when the sensitive electrode is shielded by a guard electrode, and also to have no effect on artifacts caused by body movement.

Furthermore, since the guard electrode is kept at the same potential as the sensitive electrode, no leakage current flows into the guard electrode, making it possible to make the input impedance of the electrode extremely high.

In addition, since a groove is provided between the sensitive electrode and the guard electrode, and holes are made at arbitrary points in this groove, there is no electrical contact between these electrodes due to sweat, so it can be used stably for an extremely long time. is possible.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of the biological electrode of the present invention. FIG. 2 is an equivalent circuit diagram of FIG. 1. FIGS. 3, 4, and 6 are cross-sectional views showing other embodiments of the present invention. FIG. 5 is a bottom view of the biological electrode shown in FIG. 4. FIG. 7 shows a bottom view of the biological electrode of FIG. 6. 2... Sensing electrode, 3...
・Guard electrode, 4... Electrode holder, 6...
Impedance converter, 10... groove. Figure 1 Figure 2 Figure 3 Figure 5 Figure 4 Figure 6 Figure 7

Claims (1)

[Scope of Claims] 1. A sensitive electrode attached to a living body to extract electric potential, an impedance converter that converts the biological signal extracted by the sensitive electrode into a low impedance output, and a connection to the output side of the impedance converter. A biological electrode comprising a guard electrode arranged in a ring shape and spaced apart from the sensitive electrode, and an electrode holder which exposes the biologically attached surface of the sensitive electrode and integrally holds an impedance converter and the guard electrode with an insulator. 2. A sensitive electrode attached to a living body to extract electric potential, an impedance converter that converts the biological signal extracted by the sensitive electrode into a low impedance output, and an impedance converter connected to the output side of the impedance converter and separated from the sensitive electrode. a guard electrode arranged in a ring shape, an electrode holder which exposes the biological attachment surface of the sensitive electrode and holds the impedance converter and the guard electrode together with an insulator; A biological electrode that has a groove between it and a guard electrode placed on the body, and a hole bored in any part of the groove to allow sweat generated in the living body to escape to the outside.